Lewis Base Activation of Grignard Reagents with N-Heterocyclic Carbenes.Cu-Free Catalytic Enantioselective Additions to gamma-Chloro-alpha,beta-Unsaturated Esters

摘要

Catalytic asymmetric additions of alkylmetals to allylic halides or phosphates and alpha,beta-unsaturated carbonyls are effective methods of enantioselective C-C bond formation.Such processes are carried out in the presence of a metal salt,which is nearly always Cu-based.Attributes of the in-situ-formed Cu reagent govern reactivity and selectivity.Development of Cu-free protocols is a critical step toward achieving reactivity and selectivity profiles that are inaccessible by organocopper systems.